feat(metadata): parse C2PA JUMBF manifest fields, add Images 2.0 sample, bump to 0.3.4

- metadata --check now shows claim_generator, c2pa_spec, digital_source_type,
  c2pa_actions, signer instead of empty table for C2PA-only files
- reuses existing extract_c2pa_chunk() from noai/c2pa.py — no more duplicate
  PNG chunk parsing or full-file reads
- adds data/samples/openai-images-2/amur-leopard.png: real gpt-image-2 output
  with C2PA manifest signed by OpenAI OpCo LLC / Trufo CA (spec 2.2.0)
- removes stale data/samples/nano-banana-1/2.png (no longer referenced)
- updates README: new Images 2.0 row in supported models table
- documents known text-degradation limitation in CLAUDE.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

data/samples/openai-images-2/README.md

@@ -0,0 +1,41 @@
+# OpenAI ChatGPT Images 2.0 sample
+
+Reference image generated by OpenAI's ChatGPT Images 2.0 (`gpt-image-2`, launched 2026-04-21). Kept in the repo so the C2PA manifest parser and invisible-watermark pipeline can be re-verified against a real production output.
+
+## `amur-leopard.png`
+
+- Resolution: 1055 x 1491, PNG, 3.0 MB
+- Downloaded: 2026-04-22
+- Content: AI-generated infographic about the Amur leopard (*Panthera pardus orientalis*), chosen to exercise the model's new accurate-text-rendering feature
+
+### Embedded C2PA manifest (caBX chunk, 23607 bytes)
+
+Parsed by `remove-ai-watermarks metadata --check`:
+
+| Field | Value |
+| --- | --- |
+| `claim_generator` | GPT-4o |
+| `c2pa_spec` | 2.2.0 |
+| `digital_source_type` | http://cv.iptc.org/newscodes/digitalsourcetype/trainedAlgorithmicMedia |
+| `c2pa_actions` | created, converted |
+| Signer | OpenAI OpCo, LLC / OpenAI Media Service API |
+| Claim signing CA | Trufo C2PA Claim Signing CA (2025) -> Trufo C2PA Root CA (ECC P384) |
+| Timestamp authority | OpenAI TSA Issuing CA -> OpenAI TSA Root CA |
+
+The `trainedAlgorithmicMedia` tag is what triggers "Made with AI" labels on Instagram, Facebook, and X.
+
+### Invisible pixel-level watermark
+
+OpenAI's system card for Images 2.0 states the model embeds an "imperceptible, robust, and content-specific" pixel-level watermark alongside C2PA. No public detector exists, so bypass cannot be verified empirically for this sample.
+
+## Reproducing the removal
+
+```bash
+# C2PA strip only
+remove-ai-watermarks metadata amur-leopard.png --remove -o amur-leopard.clean.png
+
+# Full pipeline (visible + diffusion regeneration + metadata)
+remove-ai-watermarks all amur-leopard.png -o amur-leopard.all.png --device mps
+```
+
+Note: the diffusion step downscales to 768 px, which degrades fine text on text-heavy infographics like this one. Tracked as a known limitation; see project TODO.